My rShaman is my alt and it's around 532ilvl now. I haven't tried speccing into the 15k haste breakpoint yet, I don't think I have the gear. That and I normally heal 10 mans. My opinion is:
- For 10mans: Spirit > Haste (7613) > Crit > Mastery > Haste
I capped my spirit at 13k. My crit with the 5% crit buff is at around 22%. My mastery is at 55% (even though on all of my gear I'm mostly reforged out of mastery) and my haste is capped at 7613. I like it this way because crit gives mana back due to resurgence. You also really don't need above 50% mastery and you will hit that point anyways even if you reforge out.
For 25mans I'm not sure because I don't really heal 25s. Stacking haste doesn't sound like a horrible idea, if you have the gear to hit the 15k~ haste breakpoint. I can imagine that would require quite a bit of gear. After that though, I'd go crit.